The manual and Powerglide will have a production
code consisting of a prefix letter designating the assembly plant, a production
date (year/month letter/day number) and a shift code for day or night shift
if the assembly plant was using two shifts.

The Turbo Hydra-Matic 400 used a different date
coding format. This production code consists of a two-digit model year (69)
followed by an engine/model code letter and a three-digit production date. The
three-digit production date begins with the first day of January 1968.
For example, a production date of 299 would be October 25, 1968 or, the
299th day of the 1968 calendar year.
(1968 was a leap year, 366 days). January 1 of 1969 would be 367.
A Julian date
calendar can be found here to assist you. Remember, a production date
of 001 to 366 is calendar year 1968
and 367 or higher is calendar year
1969. If the production date is over 366, subtract 366 and find the corresponding
Julian date for 1969. It's not known when the last TH400 was installed in
a 1969 Chevelle, but assuming July 31 the last model build day, a date of
578 should be the largest date. July 31, 1969 (578) is the 212th day of
1969. Subtracting 366 from 578 gives you 212 - July 31, 1969.

** One source shows
the letter 'D' and one source shows the letter 'O'.
Once again the coding for the Muncie 4-speed changed in 1969, but
only slightly. The basic code remained the same with the letter
designating the month and the model year was included. For example,
P9A01A breaks down to P (Muncie), 9 (1969 model
year), A (January), 01 (day), M20 . Any Muncie build in
calendar year 1968 for an August
through December built 1969 model
year would be dated with M through T (August through December) such
as P9R25A meaning the transmission was coded for a 1969 model year
Chevelle on October 25, (calendar year) 1968. A letter suffix code
was added in 1969 to identify the M20, M21, and M22 series; "A"
for the M20, "B" for the M21, or "C" for the
M22.

*** Two Protect-O-Plate cards have been contributed that show C9D03
codes for the transmission. One a Baltimore L78 4-speed and
one a Framingham L78 TH400.